The present invention generally relates to power amplifier devices, and more particularly to a power amplifier devices having a plurality of power amplifier units connected in parallel.
A communication device, such as an FM multiplex radio device or a radio device mounted on a vehicle, has a power amplifier device, which amplifies a signal having a small amount of power in order to obtain a power enough to emit a radio wave. Normally, such a power amplifier device has a plurality of power amplifier units connected in parallel, an input distributor (input power divider) and an output power combining device. An input information signal is input to the power divider, which equally distributes the power of the input information signal to the power amplifier units. Then, the power amplifier units respectively amplify the power-divided input information signals, which are input to the output power combining device, so that an amplified power great enough to transmit the input information signal can be obtained.
FIG. 1 is a block diagram of a conventional power amplifier device as described above. The power amplifier device shown in FIG. 1 includes an input distributor unit 60, four connectors 65.sub.1, 65.sub.2, 65.sub.3 and 65.sub.4, four power amplifier units 66.sub.1, 66.sub.2, 66.sub.3 and 66.sub.4, four connectors 67.sub.1, 67.sub.2, 67.sub.3 and 67.sub.4, and an output power combining unit 72.
The input distributor unit 60 is composed of a circulator 62 having an input impedance Z0, and transmission lines (TL) 63, 64.sub.1, 64.sub.2, 64.sub.3 and 64.sub.4. An input information signal applied to a terminal 61 passes through the circular 62 and the transmission line 63. The transmission line 63, which has a characteristic impedance Z1 and a length .lambda.g/4 (.lambda.g is a wavelength), functions to transform the input impedance. Then, the input information signal is divided into four signal components, which are respectively input to the power amplifier units 66.sub.1 -66.sub.4 via the transmission lines 64.sub.1 -64.sub.4 and the connectors 65.sub.1 -65.sub.4. Each of the transmission lines 64.sub.1 -64.sub.4 has the characteristic impedance Z0 and a length of .lambda.g/4. The power amplifier units 66.sub.1 -66.sub.4 respectively amplify the divided input information signal components.
The power amplifier units 66.sub.1 -66.sub.4 are respectively comprised of circulators 661.sub.1 -661.sub.4, unit amplifiers 662.sub.1 -662.sub.4, and circulators 663.sub.1 -663.sub.4. The amplified information signal components output by the power amplifier units 66.sub.1 -66.sub.4 pass through the connectors 67.sub.1 -67.sub.4 and transmission lines 68.sub.1 -68.sub.4, respectively, and are then combined with each other. Each of the transmission lines 68.sub.1 -68.sub.4 has the characteristic impedance Z0, and a length equal to .lambda.g/2. Then, the resultant input signal passes through the transmission line 69 and the circulator 70, and is output, as a transmission output signal, via a terminal 71. The transmission line 69 has the characteristic impedance Z1 and a length of .lambda.g/4. The power amplifier device shown in FIG. 1 is capable of producing a power approximately four times the power of the input information signal. Each of the transmission lines 63, 64.sub.1 -64.sub.4, 68.sub.1 -68.sub.4 and 69 is comprised of a strip line or a coaxial cable. The transmission lines 68.sub.1 -68.sub.4 and 69, and the circulator 70 form the output power combining unit 72.
The power amplifier device shown in FIG. 1 is accommodated into a rack in a radio ground station in a fixed communication system or a mobile communication system. Normally, it is not necessary for the four power amplifier units 66.sub.1 -66.sub.4 to always work. For example, when a high power is needed because of the occurrence of short-term fading, the four power amplifier units 66.sub.1 -66.sub.4 are made to operate in parallel. In a normal state, for example, three of the four power amplifier units 66.sub.1 -66.sub.4 are made to operate in parallel. When there is little traffic, for example, at night, two of the four power amplifier units 66.sub.1 -66.sub.4 are made to operate. In the above-mentioned cases, a power source is disconnected from the power amplifier units which are to be stopped (see Japanese Laid-Open Patent Publication No. 62-217708).
As shown in the above Japanese publication, the power supply to the power amplifier units which are to be stopped is simply turned OFF, and is simply turned OFF in order to turn OFF these power amplifier units. Thus, harmonic waves occur at the time of turning ON/OFF the power supply. Such harmonic waves affect the operation of the other power amplifier units and result in noise on a power supply line. Further, an abrupt change in the power supply voltage affects some circuit elements of the power supply units, and may shorten the life time thereof.